Interplay between spin dynamics and crystal field in the multiferroic compound HoMnO3

Abstract

In the multiferroic hexagonal manganite HoMnO3, inelastic neutron scattering and synchrotron based THz spectroscopy have been used to investigate the spin waves associated to the Mn order together with Ho crystal field excitations. While the Mn order sets in first below 80 K, a spin reorientation occurs below 37 K, a rare feature in the rare earth manganites. We show that several Ho crystal field excitations are present in the same energy range as the magnons, and that they are all affected by the spin reorientation. Moreover, several anomalous features are observed in the excitations at low temperature. Our analysis and calculations for the Mn spin waves and Ho crystal field excitations support Mn-Ho coupling mechanisms as well as coupling to the lattice affecting the dynamics.

Magnetic structure and multiferroicity of Sc-substituted hexagonal YbFeO3

“…Furthermore, the magnetic transition at TR ~ 40 K identified here was also reported for the h-Lu1-xScxFeO3 single crystal [17]. It is noted that all the h-RMnO3 and those h-RFeO3 containing Sc samples exhibit spin reorientation at low temperature, e.g., T = 37 K for h-HoMnO3 [39], 43.5 K for h-YbMnO3 [40], 40 K for h-LuMnO3 [41], 35 K for h-YMn0.9Fe0.1O3 [42], and 45 K for h-Lu0.5Sc0.5FeO3 [17]. The earlier neutron scattering provided clear evidence for the Mn/Fe ionic shift from the 1/3 position [17,43].…”

Efficient spin excitation via ultrafast damping-like torques in antiferromagnets

“…Ultrafast spin damping in YMnO 3 . The general trend of α is captured well by an offset Bose-Einstein distribution for a quasiparticle with an energy of~4.3 meV, suggesting that scattering with the crystal-field excitations of the Ho 4f electrons (≈3.5 meV 24 ) contributes significantly to the spin damping. This is confirmed by measurements on YMnO 3 (Fig.…”

“…All anisotropy parameters can be extracted from a fit of the temperature dependence of ω 0 with a minimal model (see Methods section). (The deviations below 25 K are caused by the incipient ordering of the Ho(4b) moments 24,31,32 , see Supplementary Fig. 3).…”

“…Furthermore λ > 0 and D z > 0 parametrise the antiferromagnetic intra-plane exchange interaction and the easy-plane anisotropy, respectively. The inter-plane exchange is two orders of magnitude weaker than the intra-plane exchange; thus, we neglect it 24 . D y < 0 stabilises the ground state as ( M i then points along equivalent crystallographic y axes), whereas D y > 0 stabilises (with M i along equivalent crystallographic x axes).…”

“…We model the SRT in HoMnO 3 by introducing a linear dependence of the anisotropy parameter D y on temperature. The SRT temperature T SR is defined as the point where D y vanishes 24 , i.e. D y ( T ) = κ ( T − T SR ).…”